1. Field of the Invention
The present invention relates to a device for removing ions in an electron accumulating ring, as well as a method thereof. The present invention also pertains to an electron accumulating ring having an ion removing device.
2. Description of the Related Art
FIG. 7 is a cross-sectional view of the essential parts of a conventional electron accumulating ring which has been introduced in, for example, proceedings of the 6th symposium on Accelerator Science and Technology held from Oct. 27th to 29th in 1987 in Tokyo on page 265 by Sugiyama and others. In the figure, reference numeral 1 denotes a vacuum container; 2 denotes a wire-like ion removing electrode provided in the vacuum container 1 to induce electrons and thereby take out ions to the outside of the ring in order to increase the life of the electrons in the vacuum container 1; 3 denotes a deflection electromagnet provided around the vacuum container 1 to generate a magnetic field in a vertical direction in order to curve electrons in a horizontal direction; 4 denotes the direction of the magnetic field; and 5 denotes the direction of an electric field. The electron accumulating ring further includes a quadrupole electromagnet provided around the vacuum container 1 to stabilize the electron orbits, and a high-frequency accelerating space for accelerating electrons, which are not shown.
In the conventional electron accumulating ring arranged in the manner described above, when a high voltage is applied to the ion removing electrode 2, an electric field is generated in direction indicated by arrows 5. Because of the generated electric field and magnetic field, the ions at the central portion perform drift motion. The direction of the drift motion is directed toward this side and in a direction perpendicular to the paper, whereby they can be taken out to the outside of the deflection electromagnet 3.
However, in the electron accumulating ring having a racetrack-like shape, the beam diameter in the horizontal direction is at a minimum near the center of the deflection electromagnet which surrounds the ring over 180.degree.. Generally, the position where the beam diameter is at a minimum is the position where the potential as seen from ions is the lowest, and the ions are trapped at that trough of the potential. FIG. 8 is a graph showing the potential generated by the charged particles which circulate the accumulating ring. In FIG. 8, the abscissa axis represents the distance in the axial direction of a beam, and the coordinate axis represents the potential. As can be seen from FIG. 8, the potential as seen from the ions is the lowest near the center of the deflection electromagnet which surrounds the ring over 180.degree.. Ions are trapped at that position.
Thus, it is impossible for the ion removing electrode 2 shown in FIG. 7 to take out the trapped ions to the outside of the deflection electromagnet 3.
Hence, the ion removing device shown in FIG. 9 has been proposed. The device shown in FIG. 9 has been described "High-Energy Accelerator Seminar" published by High-Energy Physics Association No. VI on page 17. In the figure, reference numeral 6 denotes an ion removing electrode; 7 denotes a vacuum container; and 8 denotes an electron beam.
In the ion removing device arranged in the manner described above, when the ions trapped by the potential of the electron beam 8 are present near the ion removing device, a voltage of several hundreds of volts is applied to the ion removing electrodes 6. Consequently, the ions in the vacuum container 7 constituting the electron accumulating ring move away from the potential of the electron beam 8 toward the ion removing electrodes 6. Those ions disappear at the ion removing electrodes 6. Thus, the ions in the electron accumulating ring can be removed.
However, it is difficult to provide the ion removing electrodes 6 in such a manner that they are separated in the vertical direction at the center of the deflection electromagnet, as shown in FIG. 9, because the portion of the vacuum container 7 which is located in the deflection portion is generally manufactured as one unit to obtain a super high vacuum. Furthermore, since the diameter of the electron beam in the vertical direction is at a maximum at the center of the deflection portion, the provision of the ion removing electrodes 6 in the vertical direction may prohibit stable circulation of the electron beam. Also, when the ion removing electrodes 6 are provided in the vertical direction, since the electrodes are located close to the electron beam, stable circulation of the electron beam may be prohibited due to the wake generated by the electron beam.
In order to solve the above-described problems, the ion removing electrodes 6 may be provided in such a manner that they are separated in the horizontal direction of the vacuum container 7. However, in that case, when an electric field is applied in the horizontal direction in the high magnetic field of the deflection electromagnet to remove the ions, the ions may perform drift motion in the axial direction of the beam but not be removed efficiently.
In the above-described conventional ion removing device, since the ion removing electrodes 6 are provided in the vacuum container 7 in the vertical direction, the vertical aperture of the orbit of the electron beam is narrowed, thus making stable circulation of the electrons impossible.
Furthermore, the portion of the vacuum container 7 which is located in the defection electromagnet is manufactured as one unit in order to obtain a super-high vacuum. It is therefore difficult to firmly mount the ion removing electrodes 6 in the deflection electromagnet in such a manner that they are separated in the vertical direction. Where the ion removing electrodes 6 are provided such that they extend over 180.degree., they may be fixed at the exits of the two ends of the deflection electromagnet. However, it is impossible to fix the ion removing electrodes 6 in the inside of the deflection electromagnet at the central portion thereof, and this makes it impossible to specify the position of the ion removing electrodes 6 in the deflection electromagnet after the deflection electromagnet has been incorporated.